**( pi = = 3.141592…)**

Perimeter Formulas

The perimeter of any polygon is the sum of the lengths of all the sides.

### Note: “ab” means “a” multiplied by “b”. “a^{2}” means “a squared”, which is the same as “a” times “a”.

### Be careful!! Units count. Use the same units for all measurements. Examples

**square** = 4a

**rectangle** = 2a + 2b

**triangle** = a + b + c

**circle** = *pi*d (where d is the diameter)

The perimeter of a circle is more commonly known as the circumference.

Be sure to only add similar units. For example, you cannot add inches to feet.

For example, if you need to find the perimeter of a rectangle with sides of 9 inches and 1 foot, you must first change to the same units.

perimeter = 2 ( a + b)

**INCORRECT**

perimeter = 2(9 + 1) = 2*10 = 20

**CORRECT**

perimeter = 2( 9 inches + 1 foot)

= 2( 3/4 foot + 1 foot )

= 2(1 3/4 feet)

= 3 1/2 feet

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